1. Technical Field
The present invention relates to a connecting terminal for establishing electrical connection between conductor portions of printed circuit boards disposed in a facing relation, and relates to a connecting terminal assembly comprised of a plurality of connecting terminals that are removably attached to a mount base and adapted to be mounted on printed circuit boards with use of an automatic loader.
2. Related Arts
Electronic equipment, such as personal computers and telephone sets, accommodates therein a large number of electronic component parts. Typically, these component parts are mounted on a plurality of printed circuit boards that are accommodated in a cabinet of electronic equipment. To reduce the space required for installation of the printed circuit boards in the cabinet and to facilitate easy assembly, these circuit boards are disposed in the cabinet in a facing relation to one another. In order to establish electric connection between conductive patterns respectively formed in adjacent printed circuit boards, connecting terminals, such as the one disclosed in Japanese provisional patent publication no. 9-115574, have been employed.
This conventional connecting terminal is comprised of a U-shaped metal plate fabricated by bending an elongated plate, punched out from a metal sheet having upper and lower surfaces thereof plated in advance, into a U-shape, as shown in FIG. 9. The connecting terminal, having a first contact section 51 thereof formed by a longer half of the U-shaped plate, is adapted to be soldered at this contact section 51 to a conductor pattern (not shown) of a first printed circuit board 53. To this end, a first and second soldered-connection portions 51a, 51b are formed in the contact section 51 by cutting and upwardly raising a longitudinally intermediate portion and an outer end portion of the contact section 51. These soldered-connection portions 51a, 51b of the connecting terminal 50 are soldered to the conductor pattern of the first printed circuit board 53, whereby the connecting terminal 50 is electrically and mechanically connected to the conductor pattern of the printed circuit board 53. Subsequently, a second contact section 52, formed by a shorter half of the U-shape plate, of the connecting terminal 50 is abutted against a conductor pattern formed in a second printed circuit board 54, so as to be electrically connected thereto. In this manner, electrical connection between the conductor patterns of the first and second circuit boards 53, 54 is established through the connecting terminal 50 having the first fixed-contact section 51 and the second free-contact section 52 elastically flexible relative to the contact section 51.
To ensure that the connecting terminal 50 is properly joined to the printed circuit board 53, with an intended orientation and at an intended position thereon, the soldered-connection portions 51a, 51b of the connecting terminal 50 must be separated at a distance from each other and soldering flux or paste must be applied to surface areas of the conductor pattern of the first printed circuit board 53 that are apart from each other at a distance corresponding to the distance between the soldered-connection portions 51a, 51b. This requirement must be satisfied, especially when the connecting terminal 50 is soldered to the printed circuit board 53 by reflowing-type soldering.
If the soldering-flux is applied to areas of the printed circuit board 53 which are not separated at a required distance but form a single area wide enough to cover a longitudinal zone including lengthwise portions of the circuit board 53 which respectively correspond to the soldered-connection portions 51a, 51b of the connecting terminal 50, molten solder flows into between the opposed flat surfaces of the first contact section 51 of the connecting terminal 50 and the printed circuit board 53 during the soldering process by reflowing-type soldering or the like. As a result, the connecting terminal 50 maybe in a floated state on the molten solder, since the circuit-board-side surface of the first contact section 51 is formed, as a whole, into a single flat plane. In such a floated state, the connecting terminal 50 can be directed to an unexpected orientation, and thus the connecting terminal 50 is sometimes joined, with an undesired orientation, to the printed circuit board 53 after the solder is solidified.
In surface-mounting the connecting terminal 50 to the printed circuit board 53, a suction pickup device is often employed to pick up the connecting terminal by suction and transport the same to the circuit board. In this case, an upper face of the first contact section 51 of the connecting terminal 50 serves as a pickup face against which a suction nozzle of the pickup device is positioned. At the time of picking up the connecting terminal 50, a movable part, including the suction nozzle, of the suction device is moved toward the connecting terminal 50 to permit the suction nozzle to be positioned on the pickup face. To avoid interference between the connecting terminal 50 and the movable part of the pickup device moved toward the connecting terminal 50, the second contact section 52 of the connecting terminal, extending upwardly from the first contact section 51 toward the suction device, is bent at its proximal end so as to extend at an acute angle with respect to the first contact section 51.
As the acute angle formed between the first and second contact sections 51, 52 becomes small, the vertical dimension of the connecting terminal 50 becomes smaller. In order to electrically connect the circuit boards through such a low-profile connecting terminal 50, the printed circuit boards must be disposed close to each other at a small distance. In other words, electric connection between the printed circuit boards cannot be established with use of the connecting terminal 50, if one or more electric component parts, having a height greater than that of the connecting terminal 50, are mounted to either one or both of the printed circuit boards.
Since the second contact section 52 of the connecting terminal 50 extends at an acute angle with respect to the first contact section 51, the second contact section 52 can be flexed insufficiently in the vertical direction of the connecting terminal 50 when the second printed circuit board 54 is brought in urged contact with the second contact section 52. In this case, a contact force large enough to eliminate a layer of oxide film or the like, if any, on the conductor pattern cannot be produced between a conductor pattern 54p of the printed circuit board 54 and the second contact section 52, so that defective electric connection may be caused between the printed circuit board 54 and the second contact section 52.
Furthermore, the conventional connecting terminal 50 can be unsatisfactorily sucked by the suction pickup nozzle so that it may drop therefrom during the picking-up and transfer processes, since the center of the pickup face of the first contact section 51 is deviated from the center of gravity of the connecting terminal 50 whose first contact section 51 is provided at only one end with the second contact section 52.
An object of the present invention is to provide a connecting terminal that can be easily surface-mounted on and accurately joined to a printed circuit board with an intended orientation and at an intended position thereon.
According to one aspect of the present invention, there is provided a connecting terminal, interposed between a first and second printed circuit boards facing each other, for establishing electric connection between conductor portions respectively formed in the first and second printed circuit boards.
The connecting terminal of this invention comprises a central section having a major portion thereof extending longitudinally of the connecting terminal at a vertically intermediate position in the connecting terminal, a first fixed-contact section extending outwardly longitudinally of the connecting terminal from a corresponding one of longitudinally outer ends of the central section, a second fixed-contact section extending outwardly longitudinally of the connecting terminal from the other longitudinally outer end of the central section, each of the first and second fixed-contact sections being disposed at a vertical position on the side close t the first printed circuit board with respect to the major portion of the central section and being adapted to be joined to a corresponding one of first and second conductor portions of the first printed circuit board, and at least one free-contact section extending from at least one of longitudinally outer ends of the first and second fixed-contact sections, said free-contact section extending inwardly and longitudinally of the connecting terminal and extending vertically of the connecting terminal toward the second printed circuit board, said free-contact section being adapted to be elastically flexed in the vertical direction of the connecting terminal when it is in contact with the conductor portion of the second printed circuit board.
According to the connecting terminal of this invention, in a condition that the first and second fixed-contact sections are in contact with the first and second conductor portions of the first printed circuit board, the major portion of the central section of the connecting terminal is apart from the conductor portions of the first printed circuit board as viewed in the vertical direction of the connecting terminal. In other words, the connecting terminal is formed into such a shape that a longitudinally central part of its face on the first-printed-circuit-board side is out of contact with the first printed circuit board. For this reason, in the case of soldering the connecting terminal to the first printed circuit board by means of, e.g., reflowing-type soldering, molten solder congregates, attributable to its surface tension, around locations at which the fixed-contact sections of the connecting terminal are in contact with the conductor portions of the first printed circuit board. Hence, a flow of molten solder is disconnected between the first and second conductor portions of the first printed circuit board or between the first and second fixed-contact sections of the connecting terminal, even if soldering paste or solder containing soldering paste is applied to the conductor-pattern-side face of the first printed circuit board over the entirety of a longitudinal region thereof wide enough to extend between the first and second conductor portions of the circuit board.
In this manner, molten solder does not flow between the entirety of opposed faces of the connecting terminal and the first printed circuit board, irrespective of how soldering paste or solder containing the same is applied to the circuit board. Thus, the connecting terminal will never be in a floated state on the molten solder during the soldering process. This makes it possible to join the connecting terminal to the conductor pattern of the first printed circuit board at a desired position and with a desired orientation, once the connecting terminal has been placed thereon at such a position and with such an orientation.
Upon surface-mounting the connecting terminal on the first printed circuit board, a suction pickup device is typically used to pick up the connecting terminal by suction and transfer the same to the printed circuit board. In this case, a surface of the major portion of the central section of the connecting terminal serves as a pickup face. The suction-holding of the connecting terminal may be achieved by moving a suction nozzle of the pickup device by a short distance to the major portion located at a location short of the fixed-contact sections in the vertical direction of the connecting terminal. This moderates the requirement of acutely bending the free-contact section at its proximal end relative to the associated fixed-contact section to the extent that interference between the connecting terminal and a movable part, including the suction nozzle, of the pickup device is prevented.
In this manner, the angle formed between the free-contact section and the fixed-contact section can be made relatively large, and hence the vertical distance between an outer end of the free-contact section and the fixed-contact section can be made larger. As a result, electric connection between the first and second printed circuit boards can be established with use of the connecting terminal disposed therebetween, even if the first and second printed circuit boards must be disposed at a relatively large distance for the reason that one or more large vertical-size component parts are mounted on one or both of the first and second printed circuit boards or other reasons.
In addition, the vertical distance between the outer end of the free-contact section and the fixed-contact section is large enough to permit the free-contact section to sufficiently flex around the boundary between the free-contact section and the fixed-contact section. That is, by bringing the second printed circuit board in contact with the outer end of the free-contact section and by further moving the circuit board toward the fixed-contact section, the free-contact section can be sufficiently flexed in the vertical direction of the connecting terminal. As a consequence, the free-contact section of the connecting terminal is brought into spring contact with the conductor pattern of the second printed circuit board with sufficient contact pressure, thereby establishing proper electrical connection between the connecting terminal and the second printed circuit board.
Furthermore, since the first and second fixed-contact sections are formed on the opposite ends of the major portion of the central section of the connecting terminal, the geometrical center of the major portion of the central section can be made close to the center of gravity of the connecting terminal. For this reason, when the connecting terminal is picked up by suction and transferred toward the first printed circuit board by use of a suction pickup device, while utilizing, as pickup face, the outer face of the major portion of the central section, the connecting terminal can be positively held by the suction pickup device and prevented from dropping therefrom during the suction and transfer processes.
In the present invention, preferably, the connecting terminal is fabricated by bending an elongated metal plate punched out from a metal sheet. The central section, the first and second fixed-contact sections, and the free-contact section of the connecting terminal are formed of a single piece.
With this preferred arrangement, the connecting terminal can be fabricated efficiently and easily at low cost and can be light in weight and still having required mechanical strength.
Preferably, the central section of the connecting terminal includes first and second leg portions respectively extending vertically with respect to the connecting terminal from the longitudinal ends of the major portion of the central section to inner longitudinal ends of the first and second fixed-contact sections.
With this preferred arrangement, the major portion of the central section of the connecting terminal can be positively disposed at an intermediate position in the vertical direction of the connecting terminal. This facilitates, for instance, soldering the connecting terminal to the conductor pattern of the first printed circuit board at a desired position and with a desired orientation, for the reason mentioned above.
Preferably, the at least one free-contact section is comprised of a first and second free-contact sections extending from longitudinally outer ends of the first and second fixed-contact sections, respectively.
With this preferable arrangement, the connecting terminal has the first free- and fixed-contact sections that are symmetric with the second free- and fixed contact sections with respect to the central section, so that the center of the major portion of the central section may be made closer to the centroid position of the connecting terminal. For this reason, when the connecting terminal is picked up and transferred to the first printed circuit board by use of a suction pickup device having a nozzle thereof positioned against the major portion of the connecting terminal, the connecting terminal can be prevented from dropping therefrom during the suction and transfer processes.
Preferably, the first and second fixed-contact sections are respectively formed with first and second grooves extending therethrough in the thickness direction of the fixed-contact sections.
With this preferred arrangement, when the fixed-contact sections are soldered to the conductor pattern of the first printed circuit board, molten solder flows into the grooves of the fixed-contact sections and is then solidified, so that the connecting terminal may be securely joined to the conductor pattern of the first printed circuit board.
More preferably, each of the first and second grooves is comprised of a plurality of slots.
With this preferred arrangement, an increased solder-connection area is provided by the grooves of the fixed-contact sections, so that the connecting terminal can be reliably joined to the conductor patterns of the first printed circuit board.
In the aforementioned preferred arrangement having the central section comprised of the major portion and the leg portions, preferably, the first and second grooves extend from inner longitudinal end portions of the first and second fixed-contact sections to vertical end portions, on the first printed-circuit-board side, of the first and second leg portions, respectively.
With this arrangement, a solder-connection area provided by the grooves increases, and the grooves are formed at such locations as to effectively contribute to solder connection between the connecting terminal and the conductor patterns of the first printed circuit board. This makes it possible to securely join the connecting terminal to the conductor patterns of the first printed circuit board.
According to another aspect of the present invention, there is provided a connecting terminal assembly which comprises a mount base formed with a plurality of holes which are spaced at a predetermined regular distance and to which feed pawls of an automatic loader are individually engaged, and a plurality of connecting terminals removably mounted on the mount base at the predetermined regular distance. Each of the plurality of connecting terminals is constructed in the same manner as the aforementioned connecting terminal.
With the connecting terminal assembly of this invention, connecting terminals can be automatically mounted to printed circuit boards with use of an automatic loader, without the need of a manual mounting operation. In the case of fabricating the connecting terminals by bending elongated metal plates punched from a metal sheet, these metal plates can be punched from those parts of the metal sheet which are separated from one another at a distance shorter than the distance between adjacent connecting terminals on the mount base. This makes it possible to improve the efficiency in utilizing the metal sheet, so that connecting terminals may be fabricated at low cost.
Preferably, recessed portions for receiving the plurality of connecting terminals are formed in the mount base at the predetermined regular distance.
With this arrangement, connecting terminals are positively held in the recessed portions formed in the mount base.
Preferably, a covering tape is attached to the mount base so as to cover the plurality of connecting terminals received in the recessed portions of the mount base.
With this arrangement, each of the connecting terminals can be held in the recessed portions of the mount base with reliability and can be easily dismounted therefrom while a corresponding part of the covering tape is peeled off from the mount base.